1. Field of the Invention
The present invention relates generally to multipath acquisition of dedicated traffic channels in wireless communication systems or networks.
2. Description of the Related Art
FIG. 1 is a frame structure of a dedicated traffic channel for UMTS uplink. Systems or networks designed based on third generation wireless standards such as 3GPP (UMTS) and 3GPP2 (cdma2000) use a dedicated traffic channel in the uplink for communication from mobile users (or user equipment (UE)) to the base station (or Node-B). As shown in FIG. 1, the dedicated uplink traffic channel may include two parts, a data part (Dedicated Physical Data CHannel (DPDCH) in UMTS, known as a Fundamental CHannel/Supplemental CHannel (FCH/SCH) in cdma2000), and a control part (Dedicated Physical Control CHannel (DPCCH) in UMTS, known as a pilot/power control sub-channel in cdma2000).
For the uplink DPCCH in UMTS, there are 15 slots per radio frame (i.e., processing duration corresponding to 15 slots, where the length of the frame is 38,400 chips). One radio frame is 10 ms in duration; thus each slot is 0.667 ms in duration.
The uplink DPCCH may be used to carry control information generated at Layer 1 (the physical layer). Layer 1 control information includes known pilot bits to support channel estimation for coherent detection, transmit power-control (TPC) commands, feedback information (FBI), and an optional transport-format combination indicator (TFCI). The TFCI informs the receiver about the instantaneous transport format combination of the transport channels mapped to the simultaneously transmitted uplink DPDCH radio frame.
Within each slot, the UE thus transmits pilot bits and certain control bits such as TFCI, FBI and TPC bits. Each slot has a total of ten (10) combined pilot bits and control bits. The actual combinations of bit numbers may change and may be controlled by the Radio Network Controller (RNC) at the network, for example. An example configuration may be 5 pilot bits, 2 TFCI bits, 1 FBI bits and 2 TPC bits for one slot.
The pilot bits are known to both the Node-B and the UE; the remaining control bits (TPC, FBI and TFCI) are not known to the base station (Node-B). The number of TPC bits per slot is typically either 1 or 2 bits. If there are two TPC bits in one slot, the values of the 2 bits are identical, i.e., either both TPC bits are 0 or both bits are 1. For 3GPP2 (cdma2000), the frame structure is similar to FIG. 1, although there are no TFCI and FBI bits defined in 3GPP2. For the following discussion, a conventional UMTS transmitter/receiver interface is described.
FIG. 2 is a block diagram of a conventional UMTS uplink transmitter/receiver relationship. Referring to FIG. 2, at the transmitter 200 (of the UE), the DPCCH and the DPDCH are modulated using BPSK (Binary Phase Shift Keying) at BPSK modulators 205. The DPCCH and the DPDCH are then spread by two different and orthogonal codes (Walsh codes) at 210 and weighted by corresponding gains at 215 to achieve certain power levels. The two channels are then combined (code-division multiplexed) at multiplexer 220.
The combined signal may be scrambled and filtered by a shaping filter 225 before modulated to RF (not shown for purposes of clarity) and sent through the propagation channel 230 to the base station (Node-B) receiver 250.
At the Node-B receiver 250, the received signal first passes a matched filter 255. The filtered signal may then be sent to a DPCCH and DPDCH processing block 260 to generate DPDCH soft symbols (shown generally at 262), for further processing by blocks such as turbo/convolutional decoders (not shown). The DPCCH and DPDCH processing block 260 also generates propagation channel measurements such as mobility of the UE. In FIG. 2, for example, this may be shown as a ‘binary mobility indicator’ 264, which may have a value of ‘1’ to indicate a high mobility user and a value of ‘0’ to indicate a low mobility user.
The DPCCH and DPDCH processing block 260 thus requires the knowledge of propagation paths, primarily the path positions. This knowledge is produced in the receiver 250 by a multipath acquisition block 265 and is managed by an ‘existing and new paths management’ block 270. The multipath acquisition block 265 searches a possible range of path positions (also occasionally referred to herein as ‘paths’ or ‘hypotheses’) and reports all positions that are determined as having significant signal energy, such as above some given threshold.
The existing and new paths management block 270 further screens the paths reported by the multipath acquisition block 265 and the paths that are already in use in the DPDCH and DPCCH processing block 260. The existing and new paths management block 270 removes repetitive paths and/or weak paths, adds new paths just discovered by the multipath acquisition block 265 and then passes the updated paths' information back to the DPDCH and DPCCH processing block 260. The frequency of the update can be programmable, depending on the design goals. For example, an update interval or frequency may be one DPCCH frame (10 ms). As will be seen below, conventional multipath acquisition uses only the pilot signal information in the DPCCH.
FIGS. 3A and 3B illustrate process flows for conventional multipath acquisition. In particular, FIGS. 3A and 3B generally describe the processing in multipath acquisition block 265 of FIG. 2. Referring to FIG. 3A, the pilot energy over a frame is calculated for a specific path position (hypothesis). Initially, the matched filter output from matched filter 255 corresponding to this hypothesis (which is a complex signal) is descrambled and despreaded (310). The pilot pattern is also removed by function 310 as well. The output symbols corresponding to pilot bits are next accumulated (320) by simple addition over each slot. The output of this block is at a slot rate, i.e., one (complex) output per slot.
Next, the L2-norm of the output from 320 is formed (330). Assuming for example that the complex output signal is z=a+j*b, its L2-norm may be given by L2(z)=a2+b2. The L2-norms of the accumulated pilot signal are further accumulated over the frame interval (340). The resultant output is the frame pilot energy (350).
Referring to FIG. 3B, the frame pilot energy for each hypothesis (355) is compared with a fixed pre-defined or given threshold (365). Hypotheses with frame pilot energy surpassing the threshold (output of 365 is ‘YES’) are reported (375) to the existing and new paths management block 270 in FIG. 2 for further processing.
The conventional approach suffers from detection performance issues in general, as it does not make use of the other control bits. Thus, conventional multipath acquisition processing generally requires more energy to achieve the same acquisition performance. This may cause higher interference levels for other users and may reduce system capacity. Moreover, conventional multipath acquisition is especially an issue for a UE with high mobility.